tutorny wrote: >> Think again. How would you work out the probability that exactly 30 >> left? See if your textbook has any examples like that. > > Hi Bruce, I have no clue. My book doesn't have anything even remotely > close to this. > > If I want to get exactly 30, should I do p(x<=30.5) - p(x<=29.5), > which will come to P(z <= 2.0261) - P(z <= 1.7878) = 0.9786 - 0.9631 = > 0.0155. So, P(exactly 30 left the program) = 1.55% > > And, P(x<=30) = P(x<=29.5) + P(x=30) = 0.9631 + 0.0155 = 0.9786 = > 97.86%
I didn't check your calculations, but notice that you already had the 0.9786 above as p(x <= 30.5). ;-)
> > Does that make sense? I'm so confused! > > Thanks!
Using the binomial calculator at the link given below, I get p(x <= 30) = 0.975286.... Your normal approximation is in the same ballpark.